Export constraints and inverse kinematics
FBX or collada can bake effects of the constraints while exporting animations, that’s all. There is no way to export constraint/IK systems themselves, afaik.

Further more, I’m not sure that would make sense at all, seeing how hard it is already to support basics of exchange between applications that all have different ways of handling common topics (referring to animation and armatures e.g.), I would suspect things rather complex and advanced like constraints to be a plain nightmare.